The present invention relates to a high pressure fuel pump for providing a high pressure supply of fuel to the fuel injection valve of the engine.
A high pressure fuel pump for a car engine known in the prior art is a variable delivery type fuel pump wherein a solenoid is used to control the time of opening or closing an intake valve and the amount of fuel to be delivered is variably adjusted. An example is found in an apparatus disclosed in the specification of the International Publication Number WO00/47888.
The aforementioned example will be described below: When the solenoid is turned off, an intake valve is pushed open by an engaging member provided with energizing force by a spring, and is kept open So that the solenoid turned on. This generates force greater in the direction reverse to the aforementioned energizing force, wherein this generated force is greater than the aforementioned energizing force. In this manner, the intake valve is closed. This step controls the intake valve opening/closing time interval, whereby the amount of delivery is controlled, according to said prior art.
However, when the aforementioned prior art high pressure fuel pump is used, the intake valve is forcibly closed by the pressure of the fuel flowing backward of the intake valve, even if an attempt is made by the engaging member to keep the intake valve open in the delivery stroke of the pump in the case of a high flow rate as in high-speed rotation. Thus, over a certain rotational speed, control of the amount of delivery is difficult in this type of prior art pump. This problem can be solved by increasing the force of a spring for energizing the engaging member. However, depending on the size, the solenoid is limited in the capacity to generate force. So a small solenoid cannot lift the engaging member, and the amount of delivery cannot be controlled in the case of a compact configuration. Further, when the pump displacement volume is to be increased, there is a further increase in the flow rate in passing through the intake valve, with the result that the rotation speed at which the amount of delivery can be controlled is further reduced. An actual car is required to provide a large-volume fuel pump with a high degree of displacement.
Further, a high speed type engine and multiple cylinder engine such as V8 and V10 is required to contain a solenoid capable of providing a high degree of response. However, the aforementioned prior art high pressure fuel pump has failed to give a sufficient consideration to ensure a highly responsive solenoid. In a single cylinder plunger type which is a current mainstream of the high pressure fuel pump, the number of plunger reciprocating motions must be increased in proportion to the number of engine cylinders in order to be synchronized with the fuel injection valve, because this reduces the control cycle.
The object of the present invention is to provide a variable delivery type high pressure fuel pump, which permits the amount of delivery to be controlled even in the case of a high flow rate, and which can be mounted on a high speed engine and a multiple cylinder engine to ensure that the amount of delivery is controlled at a high degree of response.
The high pressure fuel pump according to the present invention is a variable delivery type high pressure fuel pump comprising;
A variable delivery type high pressure fuel pump comprising:
a pressure chamber leading to a fuel intake passage and a delivery passage;
a plunger that makes a reciprocating motion in said pressure chamber;
an intake valve inserted in said intake passage;
a delivery valve inserted in said delivery passage; and
an engaging member driven by said actuator so as to give an energizing force to said intake valve; wherein the time interval of opening and closing said intake valve is controlled by an actuator operated by external force;
said high pressure fuel pump characterized by further comprising
a hydraulic pressure mechanism for holding said intake valve opened with said engaging member according to no input to said actuator.
Preferably the aforementioned high pressure fuel pump is characterized by further comprising a hydraulic displacement magnifying mechanism for magnifying said actuator displacement; wherein said hydraulic displacement magnifying mechanism gives energizing force to said intake valve.
More preferably, the aforementioned high pressure fuel pump is characterized in that this pump comprises a casing for storing the aforementioned actuator and hydraulic displacement magnifying mechanism, and the thermal expansion of this casing is selected in such a way that the total thermal expansion of the actuator and hydraulic displacement magnifying mechanism in the direction of displacement transfer is approximately the same as the thermal expansion of the aforementioned casing.
More preferably, the aforementioned high pressure fuel pump is characterized in that;
The aforementioned hydraulic displacement magnifying mechanism is configured to convert a small displacement of a large-diameter bellows into a large displacement of a small diameter bellows through working fluid enclosed in bellows; and
the aforementioned large-diameter bellows is used at all times as it is compressed in the direction of displacement transfer with respect to the state of free length under no-load conditions in order to ensure that the pressure of this working fluid works at a positive value maintained at all times.
In another embodiment of the high pressure fuel pump according to the present invention, the aforementioned actuator is made of a piezoelectric element, electrostrictive element or magnetostrictive element. The aforementioned engaging member is configured to push to open the intake valve if there is no input to the actuator. Upon entry of an input to the aforementioned actuator, the actuator pulls the large-diameter bellows to pull in the engaging member that displaces integrally with the small diameter bellows, and releases engagement with the intake valve so that the intake valve can be closed.
Still more preferably, the aforementioned high pressure fuel pump is characterized by input voltage control method in such a way that;
after the input voltage given to the aforementioned actuator has been turned on, the actuator is kept turned on while the pressure in the pressure chamber remains as high as the pressure on the downstream side of the delivery passage; and,
after the plunger has started intake stroke and the pressure in the pressure chamber has started to decrease, input voltage is reduced to move the engaging member close to the intake valve, and the engaging member is engaged with the intake valve by the time the intake valve starts to open, whereby the intake valve is energized in the direction of opening the valve.